The Homer Powley "Rounded Flat Base" projectile is the same the G1 or Gavre standard projectile that were being tested at the end of the 19th and the start of the 20th century. In 1900, Colonel James Ingalls published his Ingall's tables and in 1909 the British Ballistics Tables of 1909 were published for a projectile of very similar shape. As a result, these tables were used to predict the ballistic performance of practically every bullet type made up to WWII. Even now, the ballistic coefficients given by bullet makers almost always refers to the G1 projectile, even though this ballistic coefficient is highly velocity dependent due to the very different shape of the bullets in the box compared to the G1 projectile. These days, with the increase in long range precision shooting and the availability of computer number crunching power, other drag shapes  as used in this program  are being increasingly contemplated.
The program uses second order polynomial drag functions, which were fitted to the Ingall's Tables data, to calculate the drag for a given velocity. Those functions are as follows:

